In the manufacture of integrated circuits (ICs) and other electronic devices, testing with automatic test equipment (ATE) is performed at one or more stages of the overall process. Special handling apparatus is used which places the device to be tested into position for testing. In some cases, the special handling apparatus may also bring the device to be tested to the proper temperature and/or maintain it at the proper temperature as it is being tested. The special handling apparatus is of various types including “probers” for testing unpackaged devices on a wafer and “device handlers” for testing packaged parts; herein, the terms “handling apparatus” or “peripherals” will be used to refer to all types of such apparatus. The electronic testing itself is provided by a large and expensive ATE system which includes a test head which is required to connect to and dock with the handling apparatus. The Device Under Test (DUT) requires precision, high-speed signals for effective testing; accordingly, the “test electronics” within the ATE which are used to test the DUT are typically located in the test head which must be positioned as close as possible to the DUT. The test head is extremely heavy, and as DUTs become increasingly complex with increasing numbers of electrical connections, the size and weight of test heads have grown from a few hundred pounds to presently as much as two or three thousand pounds. The test head is typically connected to the ATE's stationary mainframe by means of a cable, which provides conductive paths for signals, grounds, and electrical power. In addition, the test head may require liquid coolant to be supplied to it by way of flexible tubing, which is often bundled within the cable. Further, certain contemporary test heads are cooled by air blown in through flexible ducts or by a combination of both liquid coolants and air. In the past, test systems usually included a mainframe housing power supplies instruments, control computers and the like. Electrical cables coupled the mainframe electronics to “pin electronics” contained in the test head. Several contemporary systems now place virtually all of the electronics in the movable test head while a mainframe may still be employed to house cooling apparatus, power supplies, and the like.
In testing complex devices, hundreds or thousands of electrical connections have to be established between the test head and the DUT. These connections are accomplished with delicate, densely spaced contacts. In testing unpackaged devices on a wafer, the actual connection to the DUT is typically achieved with needle-like probes mounted on a probe card. In testing packaged devices, it is typical to use a test socket mounted on a “DUT board.” In either case, the probe card or DUT board is usually fixed appropriately to the handling apparatus, which brings each of a number of DUTs in turn into position for testing. In either case the probe card or DUT board also provides connection points with which the test head can make corresponding electrical connections. The test head is typically equipped with an interface unit that includes contact elements to achieve the connections with the probe card or DUT board. Typically, the contact elements are spring loaded “pogo pins.” Overall, the contacts are very fragile and delicate, and they must be protected from damage.
Test head manipulators may be used to maneuver the test head with respect to the handling apparatus. Such maneuvering may be over relatively substantial distances on the order of one meter or more. The goal is to be able to quickly change from one handling apparatus to another or to move the test head away from the present handling apparatus for service and/or for changing interface components. When the test head is held in a position with respect to the handling apparatus such that all of the connections between the test head and probe card or DUT board have been achieved, the test head is said to be “docked” to the handling apparatus. In order for successful docking to occur, the test head must be precisely positioned in six degrees of freedom with respect to a Cartesian coordinate system. Most often, a test head manipulator is used to maneuver the test head into a first position of coarse alignment within approximately a few centimeters of the docked position, and a “docking apparatus” is then used to achieve the final precise positioning. Typically, a portion of the docking apparatus is disposed on the test head and the rest of it is disposed on the handling apparatus. Because one test head may serve a number of handling apparatuses, it is usually preferred to put the more expensive portions of the docking apparatus on the test head. The docking apparatus may include an actuator mechanism which draws the two segments of the dock together, thus docking the test head; this is referred to as “actuator driven” docking. The docking apparatus, or “dock” has numerous important functions, including: (1) alignment of the test head with the handling apparatus, (2) pulling together, and later separating, the test head and the handling apparatus, (3) providing pre-alignment protection for electrical contacts, and (4) latching or holding the test head and the handling apparatus together.
According to the inTEST Handbook (5th Edition © 1996, inTEST Corporation), “Test head positioning” refers to the easy movement of a test head to a handling apparatus combined with the precise alignment to the handling apparatus required for successful docking and undocking. A test head manipulator may also be referred to as a test head positioner. A test head manipulator combined with an appropriate docking means performs test head positioning. This technology is described, for example, in the aforementioned inTEST Handbook. This technology is also described, for example, in U.S. Pat. Nos. 5,608,334, 5,450,766, 5,030,869, 4,893,074, 4,715,574, and 4,589,815, which are all incorporated by reference for their teachings in the field of test head positioning systems. The foregoing patents relate primarily to actuator driven docking. Test head positioning systems are also known where a single apparatus provides both relatively large distance maneuvering of the test head and final precise docking. For example, U.S. Pat. No. 6,057,695, Holt et al., and U.S. Pat. Nos. 5,900,737 and 5,600,258, Graham et al., which are all incorporated by reference, describe a positioning system where docking is “manipulator driven” rather than actuator driven. However, actuator driven systems are the most widely used, and the present invention is directed towards them.
In the typical actuator driven positioning system, an operator controls the movement of the manipulator to maneuver the test head from one location to another. This may be accomplished manually by the operator exerting force directly on the test head in systems where the test head is fully balanced in its motion axes, or it may be accomplished through the use of actuators directly controlled by the operator. In several contemporary systems, the test head is maneuvered by a combination of direct manual force in some axes and by actuators in other axes.
In order to dock the test head with the handling apparatus, the operator must first maneuver the test head to a “ready to dock” position, which is close to and in approximate alignment with its final docked position. The test head is further maneuvered until it is in a “ready to actuate” position where the docking actuator can take over control of the test head's motion. The actuator can then draw the test head into its final, fully docked position. In doing so, various alignment features provide final alignment of the test head. A dock may use two or more sets of alignment features of different types to provide different stages of alignment, from initial to final. It is generally preferred that the test head be aligned in five degrees of freedom before the fragile electrical contacts make mechanical contact. The test head may then be urged along a straight line, which corresponds to the sixth degree of freedom, that is normal to the plane of the interface (typically the plane of the probe card or DUT board); and the contacts will make connection without any sideways scrubbing or forces which can be damaging to them.
As the docking actuator is operating, the test head is typically free to move compliantly in several if not all of its axes to allow final alignment and positioning. For manipulator axes which are appropriately balanced and not actuator driven, this is not a problem. However, actuator driven axes generally require that compliance mechanisms be built into them. Some typical examples are described in U.S. Pat. No. 5,931,048 to Slocum et al and U.S. Pat. No. 5,949,002 to Alden. Often compliance mechanisms, particularly for non-horizontal unbalanced axes, involve spring-like mechanisms, which in addition to compliance add a certain amount of resilience or “bounce back.” Further, the cable connecting the test head with the ATE mainframe is also resilient. As the operator is attempting to maneuver the test head into approximate alignment and into a position where it can be captured by the docking mechanism, he or she must overcome the resilience of the system, which can often be difficult in the case of very large and heavy test heads. Also, if the operator releases the force applied to the test head before the docking mechanism is appropriately engaged, the resilience of the compliance mechanisms may cause the test head to move away from the dock. This is sometimes referred to as a bounce back effect.
U.S. Pat. No. 4,589,815, to Smith, discloses a prior art docking mechanism. The docking mechanism illustrated in FIGS. 5A, 5B, and 5C of the '815 patent uses two guide pin and hole combinations to provide final alignment and two circular cams. When the cams are rotated by handles attached to them, the two halves of the dock are pulled together with the guide pins becoming fully inserted into their mating holes. A wire cable links the two cams so that they rotate in synchronism. The cable arrangement enables the dock to be operated by applying force to just one or the other of the two handles. The handles are accordingly the docking actuator in this case.
The basic idea of the '815 dock has evolved as test heads have become larger into docks having three or four sets of guide pins and circular cams interconnected by cables. FIGS. 1A, 1B, 1C, and 1D of the present application illustrate a prior art dock having four guide-pin and hole combinations and four circular cams, which is described in more detail later. Although such four point docks have been constructed having an actuator handle attached to each of the four cams, the dock shown incorporates a single actuator handle that operates a cable driver. When the cable driver is rotated by the handle, the cable is moved so that the four cams rotate in a synchronized fashion. This arrangement places a single actuator handle in a convenient location for the operator. Also, greater mechanical advantage can be achieved by appropriately adjusting the ratio of the diameters of the cams to the diameter of the cable driver.
The docks described in U.S. Pat. Nos. 5,654,631 and 5,744,974 utilize guide pins and holes to align the two halves. However, the docks are actuated by vacuum devices, which urge the two halves together when vacuum is applied. The two halves remain locked together so long as the vacuum is maintained. However, the amount of force that can be generated by a vacuum device is limited to the atmospheric air pressure multiplied by the effective area. Thus, such docks are limited in their application.
The docks disclosed in U.S. Pat. Nos. 5,821,764, 5,982,182, and 6,104,202 use other techniques, such as kinematic couplings, to provide the final alignment between the two halves. Coarse alignment pins may also be utilized to provide an initial alignment. The coarse alignment pins may be provided with a catch mechanism, which captures the guide pin in its hole and prevents it from escaping. The catch mechanism appears to activate automatically in the '764 and '202 patents; whereas, a motor driven device is utilized for each of the three coarse alignment pins in the '182 patent. Also in the '182 patent the three motors may be operated separately to effect planarization between the docked components. In all three patents, a linear actuator is used to finally pull the two halves together. The linear actuator is disclosed as being of the pneumatic type. In docks of this type, it is necessary that another mechanism be used to provide enough pre-alignment to prevent damage to the fragile electrical contacts. For this reason the aforementioned coarse alignment pins are used, which adds to the overall cost and complexity. Thus, two sets of alignment features are provided, namely: (1) coarse alignment pin-hole combinations, and (2) a kinematic coupling. The cam-actuated docks, mentioned previously and to be described next, combine pre-alignment with gussets and cams, precision alignment with guide pins and receptacles, and mechanical advantage and locking with cams and cam followers, in three simple mechanisms. It would be desirable to retain this simplicity and proven techniques in a powered dock for large test heads.
More specifically, with regards to kinematic couplings, the '182 patent discloses that the combination of a ball and groove is termed a “kinematic contact” because such a combination provides some of the contacts needed to form the kinematic coupling. Each side of a groove is termed a “kinematic surface” because it provides for contact at a single point. The ball is called a “kinematic mating surface” because it contacts a kinematic surface at only one point. For satisfactory operation of a kinematic coupling, the '182 patent indicates that it is not necessary that grooves be used to form the kinematic surfaces. Other shapes, such as a gothic arch, can be used as well. It is also not necessary that a ball be used as the kinematic mating surface. Other shapes, such as the tip of a cone, can be made to contact a surface at a single point. Likewise, it is not necessary that each kinematic contact include two kinematic surfaces. Examples of other suitable kinematic contacts are: a ball pressing against a flat surface (one kinematic surface per contact); a ball pressing against a tetrahedron (three kinematic surfaces per contact) or a ball pressing against three balls (three kinematic surfaces per contact). Different types of contacts may be used in one coupling as long as there are six kinematic surfaces in total.
Selected details of the construction and operation of the prior art dock illustrated in FIGS. 1A through 1D are herein described. This description includes aspects from an earlier docking apparatus described in U.S. Pat. No. 4,589,815, which is incorporated by reference.
FIG. 1A shows in perspective a test head 100 held in a cradle 190, which is in turn supported by a test head manipulator (not shown). Also shown is a cut away segment of a handler apparatus 108 to which the test head 100 may be docked. FIG. 1B shows device handler 108 in somewhat larger scale and greater detail. (In this particular example the handler apparatus is a packaged device handler, and the test head is docked to it from below.) Briefly looking ahead to the sectional view in FIG. 1C, it is seen that the test head 100 has electrical interface 126, and the handler apparatus 108 has a corresponding electrical interface 128. Electrical interfaces 126 and 128 typically have hundreds or thousands of tiny, fragile electrical contacts (not shown) that must be precisely engaged in a manner to provide reliable corresponding individual electrical connections when the test head is finally docked. As is shown in this exemplary case, the lower surface of handler apparatus 108 contains the handler electrical interface 128, and the test head 100 is docked with a generally upward motion from below. Other orientations are possible and known including, but not limited to: docking to a top surface with a downward motion, to a vertical plane surface with horizontal motion, and to a plane that is at an angle to both the horizontal and vertical.
Returning to FIGS. 1A and 1B, the complete four point docking apparatus is shown; portions of it are attached either to the handler apparatus 108 or to the test head 100. Attached to test head 100 is faceplate 106. Four guide pins 112 are attached to and located near the four corners of faceplate 106. Face plate 106 has a central opening and is attached to test head 100 so that the test head electrical interface 126 (not shown in FIGS. 1A and 1B) projects through the opening and guide pins 112 define an approximate rectangle that has an approximate common center with electrical interface 126.
Gusset plate 114 is attached to the lower surface of the handler apparatus 108. Gusset plate 114 has a central opening and is attached to handler apparatus 108 so that the handler electrical interface 128 projects through the opening. Four gussets 116 are attached to gusset plate 114, one located near each of its four corners. Each gusset 116 has a guide pin hole or receptacle 112a bored in it. Each guide pin hole 112a corresponds to a respective guide pin 112. These are arranged so that when the test head is fully docked, each guide pin 112 will be fully inserted into its respective guide pin hole 112a. The fit of each guide pin 112 in its corresponding hole 112a is a close fit. Thus, the guide pins 112 and guide pin holes 112a provide alignment between the test head 100 and the handler apparatus 108.
Four docking cams 110 are rotatably attached to the face plate 106. Cams 110 are circular and are similar to those described in the '815 patent. In particular each has a side helical groove 129 around its circumference with an upper cutout 125 on the upper face. Each docking cam 110 is located in proximity to a respective guide pin 112 such that it is generally centered on a line extending approximately from the center of the test head electrical interface 126 through the respective guide pin 112 such that guide pin 112 lies between cam 110 and the test head electrical interface 126. The gussets 116 and the corners of the gusset plate 114 have circular cutouts such that when the guide pins 112 are fully inserted into guide pin holes 112a in the gussets, the circumference of each cam 110 is adjacent to and concentric with the circular cutout in its respective gusset 116. This arrangement provides an initial course alignment between the docking components as the test head 100 is first maneuvered into position for docking with handler apparatus 108. Initial coarse alignment may also be provided by the tapered ends of guide pins 112 entering their respective receptacles 112a. The gussets 116, cams 110, and guide pins 112 are arranged so that handler electrical interface 128 is kept separated from test head electrical interface 126 (not shown in FIGS. 1A and 1B) until the guide pins 112 are actually received in their respective guide pin holes 112a. Thus, pre-alignment protection is provided to the electrical contacts.
Thus, two sets of alignment features are provided, namely: (1) the fit of gussets 116 with respect to cams 110, and (2) the guide pin 112 and receptacle 112a combinations.
A circular cable driver 132 with an attached docking handle 135 is also rotatably attached to face plate 106. Docking cable 115 is attached to each of the cams 110, and to cable driver 132. Pulleys 137 appropriately direct the path of the cable to and from cable driver 132. Cable driver 132 can be rotated by means of applying force to handle 135. As cable driver 132 rotates it transfers force to cable 115 which in turn causes cams 110 to rotate in synchronism.
Extending from the circular cutout of each gusset 116 is a cam follower 111. Cam follower 111 fits into the upper cutout on the upper face of its respective cam 110. FIG. 1C shows in cross section one stage in the process of docking test head 100 with handler apparatus 108. Here guide pins 112 are partially inserted into guide pin holes 112a in gussets 116. It is noted that in this exemplary case, guide pins 112 are tapered near their distal ends and are of constant diameter nearer to their point of attachment to face plate 106. In FIG. 1C guide pins 112 have been inserted into guide pin holes 112a to a point where the region of constant diameter is just entering the guide pin holes 112a. Also in FIG. 1C, each cam follower 111 has been inserted into the upper cutout 125 on the upper face of its respective cam 110 to a depth where it is at the uppermost end of the helical cam groove 129. In this configuration, the dock is ready to be actuated by applying force to the handle 135 (not shown in FIG. 1C) and rotating the cams 110. Accordingly, this configuration may be referred to as the “ready to actuate” position. It is important to note that in this position, alignment in five degrees of freedom has been achieved. In particular, if the plane of the handler apparatus electrical interface 126 is the X-Y plane of three dimensional interface, guide pins 112 having their full diameter inserted into receptacles has established X, Y, and theta Z alignment. Furthermore, the insertion of cam followers 111 fully into all cut outs 125 has established planarization between the handler apparatus electrical interface 126 and the test head electrical interface 128.
FIG. 1D shows in cross section the result of fully rotating cams 110. The test head 100 is now “fully docked” with handler apparatus 108. It is seen that cams 110 have been rotated and have caused cam followers 111 to follow the helical grooves 129 to a point in closer proximity to faceplate 106. In addition, guide pins 112 are fully inserted into their respective guide pin holes 112a. It is observed that the closeness of the fit between the constant diameter region of guide pins 112 and the sides of the respective guide pin holes 112a determines the final alignment between the handler electrical interface 128 and the test head electrical interface 126. Accordingly, a close fit is generally required to provide repeatability of docked position within three to seven thousandths of an inch. Furthermore, the guide pins 112 must be precisely placed on face plate 106 with respect to the gussets once gusset plate 114 has been attached to handler apparatus 108. To facilitate this, the guide pins 112 may be attached in a manner that allows their position to be adjusted. A manner of doing this which is widely practiced is described in the '815 patent.
It is useful to review some information about the movement of the cam followers. FIG. 2 illustrates the vertical position of the cam follower 111 at various points of cam 110 motion. FIG. 2 applies to circular (or cylindrical) cams as well as to linear cams as used in certain docking apparatus manufactured by, for example, Reid Ashman Manufacturing Co. The shapes of the cam groove 129 and cut out 125 are schematically shown; FIG. 2 is not drawn to scale as its purpose is illustrative. The cut out area where the cam follower 111 can enter or exit the cam groove is indicated at point O. The cam follower 111 (illustrated as a dotted circle at various points in cam groove 129) enters the cut out 125 at position 400, and subsequently reaches position 410 corresponding to a “ready to actuate” position. The cut out area is connected to a generally horizontal region of groove 129 between points O and A. This horizontal region is generally one to two cam follower diameters in length (but may sometimes be less) and represents only a small portion (a few degrees) of the total cam motion. Once the cam follower 111 has been inserted to the bottom of the cut out 125, the cam may be rotated to “capture” the cam follower in this horizontal region. The cam follower 111 is “captured” at position 420. At point A the horizontal groove transitions to a sloping groove as the cam is moved further. As the cam is moved the cam follower is accordingly raised or lowered vertically. At point B at the lower end of the slope the groove transitions to a generally horizontal region that is typically at least one or two cam follower diameters long. In this latter region, the cam follower is at the extent of its travel, and the apparatus is fully docked. The apparatus is considered to be latched (or alternatively fully docked and locked) when the cam follower is at point C (illustrated with cam follower 111 at position 440), the furthest extent of the groove. The region from A to B may be referred to as the “midway” region (illustrated with cam follower 111 at position 430), and the region from B to C may be referred to as the docked region.
In light of the foregoing discussion, it is now appropriate to more fully discuss the docking process and define certain terms. The purpose of docking is to precisely mate the test head electrical interface 126 with the handler apparatus electrical interface 128. Each electrical interface 126 and 128 defines a plane, which is typically, but not necessarily, nominally parallel with the distal ends of the electrical contacts. When docked these two planes must be parallel with one another. In order to prevent damage to the electrical contacts, it is preferred to first align the two interfaces 126 and 128 in five degrees of freedom prior to allowing the electrical contacts to come into mechanical contact with one another. If in the docked position the defined planes of the interfaces are parallel with the X-Y plane of a three dimensional Cartesian coordinate system, alignment must occur in the X and Y axes and rotation about the Z axis (Theta Z), which is perpendicular to the X-Y plane, in order for the respective contacts to line up with one another. Additionally, the two planes are made parallel by rotational motions about the X and Y axes. The process of making the two electrical interface planes parallel with one another is called “planarization” of the interfaces; and when it has been accomplished, the interfaces are said to be “planarized” or “co-planar.” Once planarized and aligned in X, Y and Theta Z, docking proceeds by causing motion in the Z direction perpendicular to the plane of the handler electrical interface 128. In the process of docking, test head 100 is first maneuvered into proximity of the handler 108. Further maneuvering brings the circular cutouts of the gussets 116 into a first alignment with the cams 110. This position, or one just prior to it, may be considered to be a “ready to dock” position. More generally, “ready to dock” refers to a position where some first coarse alignment means is approximately in position to be engaged. At this stage and depending upon design details, the distal end of the guide pins are ready to enter their respective guide receptacles. Still further maneuvering will bring the test head to a “ready to actuate position,” which was defined previously in terms of FIGS. 1A through D. More generally, “ready to actuate” refers to a position where a test head has achieved a position where a docking apparatus may be actuated. At the ready to actuate position, approximate planarization and alignment in X, Y and Theta Z have been achieved. As the dock is actuated and the guide pins 112 become more fully inserted into their respective guide-pin holes 112a, alignment and planarization become more precise. It is noted that in manipulator driven docking, as described in the '258 and '737 patents, sensors detect the equivalent of a ready to actuate position in order to change from a coarse positioning mode to a fine positioning mode. Thus, to one of ordinary skill in the art, sensing a ready to actuate position in an actuator driven dock would be a natural extension (intuitive and obvious) of what is taught and disclosed by the '258 and '737 patents.
Docks of the type described above have been used successfully with test heads weighing up to and over one thousand pounds. However, as test heads have become even larger and as the number of contacts has increased, a number of problems have become apparent. First, the force required to engage the contacts increases as the number of contacts increases. Typically a few ounces per contact is required; thus docking a test head having 1000 or more contacts requires in excess of 100 or 200 pounds for this purpose. With test heads occupying a volume of approximately a cubic meter or more, it becomes increasingly difficult for the operators to observe all of the gussets and cams to determine when the test head is in a ready to dock and the ready to actuate positions. Also due to the resiliency of the compliance mechanisms and cable in the test head manipulator, the bounce back effect has made it difficult to maintain the test head in the ready to actuate position while simultaneously initiating the actuation. A further difficulty that arises from the increased amount of force to be overcome by the actuation mechanism is that the cam motion can become unsynchronized due to the stretching of the cable. A similar problem of mechanism distortion is known in docks using solid links and bell cranks.
Docking apparatus such as described above may be characterized by the number of guide pins and receptacles used. The apparatus described in the '815 patent is characterized as a two-point dock, and the apparatus shown in FIGS. 1A through 1D is known as a four point dock. Three point docks following the same general principles are also known and in common use. The present invention will be described in terms of a four-point configuration, however, this does not limit its application to other configurations.